The present invention generally relates to a light source apparatus including light-emitting devices such as light-emitting diodes as a light source thereof, and particularly to a light source apparatus suitable for the application to an illumination light source capable of obtaining a white surface light source by equally diffusing and energizing light-emitting diodes of three colors of R (red), G (green) and B (blue). Also, the present invention relates to a display apparatus including a light source apparatus for illuminating a display portion from the back.
As a use of a light-emitting diode (LED), there is known a white LED capable of emitting white light by combining a plurality of white light-emitting diodes (white LEDs) with light-emitting diodes of three colors of R (red), G (green) and B (blue) or light-emitting diodes of other colors.
As light-emitting diodes become more powerful in recent years, a use of this white LED light source is being widely spread.
In particular, it has been considered that the white LED light source may be applied to backlights of illumination light sources, projector light sources and large-sized liquid-crystal displays. In these uses, because light-emitting diodes are featured in that they are free from mercury, small in environmental load, excellent in color reproducibility, excellent in responsiveness, have brightness variability and that they are long in service life, the white LED light source may be expected as a white light source which can replace related-art fluorescent tubes (hot cathode tube and cold cathode tube).
When the white LED light source is applied to the backlights of the above-mentioned illumination light source, projector light source and large-sized liquid-crystal display, in order to achieve required brightness to provide a surface light source, it is necessary to use a large number of light-emitting diodes which are point sources of light at present. Also, it is requested that unevenness in brightness and unevenness in chromaticity of the whole of the surface light source should be controlled so as to fall within predetermined ranges.
Two types of backlights, that is, an edge-light type backlight and a direct type backlight are known as typical backlight structures using light-emitting diodes.
The edge-light type backlight include light-emitting diodes to emit light onto an end face of a light guide plate provided on the lower surface of a diffuser from the direction perpendicular to the illumination direction thereby to provide a surface light source.
The direct type backlight includes light-emitting diodes located just under the diffuser in an XY matrix fashion (that is, in a two-dimensional fashion) to emit light in the direction vertical to the diffuser to thereby provide a surface light source.
According to the edge-light type backlight, light guided to the light guide plate from the light source located in the lateral direction of the screen is changed in direction toward the front of the screen by a diffusing sheet or a reflective sheet.
However, luminous efficiency is unavoidably lowered because a quantity of light is considerably decreased by a loss of light during the direction of traveling light is changed and hence brightness tends to be lowered at the position distant from the light source.
For this reason, the edge-light type backlight is employed by relatively small-sized backlights.
On the other hand, the direct type backlight is suitable for use with relatively large-sized backlights.
However, since a length of a light path ranging from the light-emitting diodes to the diffuser plate is reduced as compared with the edge-light type backlight under the condition that the thickness of the backlight is limited, it is comparatively difficult to uniformly disperse lights from the respective light-emitting diodes into the plane.
Then, while the direct type backlight has an advantage in which brightness can be increased easily, it has drawbacks in which unevenness in brightness and unevenness in chromaticity tend to occur.
On the other hand, in the direct type backlight, there are known methods for uniformly dispersing lights from the respective light-emitting diodes into the plane within a range of a limited thickness of the backlight.
For example, known methods are:
(1) To increase a diffusing rate of the diffuser;
(2) To dispose a large number of small-sized light-emitting diodes; and
(3) To dispose optical members capable of diffusing lights emitted from respective light-emitting diode light sources in the lateral direction on respective light-emitting diodes.
However, when the above-mentioned method (1) for increasing the diffusing rate of the diffuser is used, since transmittance of the diffuser is lowered, a utilization factor of light is lowered and as a result it is unavoidable that electric power required to obtain predetermined brightness is increased. Also, according to this method (1), there are limits in effects for improving unevenness in brightness and unevenness in chromaticity.
For this reason, it is desirable to use the method (2) to dispose a large number of small-sized light-emitting diodes and the method (3) to dispose optical members capable of diffusing lights emitted from respective light-emitting diode light sources in the lateral direction on respective light-emitting diodes.
According to any of the methods (1) to (3), when a white light source is provided by a combination of light-emitting diodes of three colors of R, G and B or light-emitting diodes of other colors, arrangements of light-emitting diodes of respective colors and optical radiation characteristics should be considered in such a manner that respective color may become white surface light sources without unevenness in brightness and unevenness in chromaticity within a predetermined visual field angle on the whole surface of the panel of the backlight.
An arrangement using a lens or a substantially conical reflective surface is known as an arrangement using the above-mentioned method (3) to dispose optical members capable of diffusing lights emitted from respective light-emitting diode light sources in the lateral direction on respective light-emitting diodes. See, Japanese Published Utility Model Application No. 7-3154 and Japanese Published Utility Model Application No. 2004-140324.
In particular, according to the arrangement using the substantially conical reflective surface, since light emitted from the light-emitting diode is changed to substantially the lateral direction to extend the light path length and the light-emitting direction is changed again to the backlight panel direction by suitable devices such as the diffuser and a brightness increasing film, unevenness in brightness and unevenness in chromaticity between the respective light-emitting diodes can be dispersed satisfactorily.
Further, it is possible to construct a light-emitting diode package (LED package) by the light-emitting diodes and the substantially conical reflective surface.
Then, there is proposed an LED package in which the package having the above-mentioned arrangement is applied to the white light source using the light-emitting diodes of three colors of R, G and B. See, Japanese Published Patent Application No. 2004-140327.
When the backlight is configured by the white light source composed of the light-emitting diodes of three colors of R, G and B, the light-emitting diodes of respective emitted colors should be energized in order to obtain a white color of desired color temperature. To this end, the light-emitting diode of each color should be energized with brightness matched with a predetermined brightness ratio determined by a light-emission wavelength.
However, since luminous efficiency of the light-emitting diode differs in emitted light of each color, the light-emitting diodes of other light-emission colors should be energized at a decreased output in harmony with a light-emitting diode of light-emission color of which rated light-emission brightness ratio relative to required brightness is lowest.
As a result, since light of color with satisfactory luminous efficiency is unavoidably emitted at light-emission brightness lower than the rated light-emission brightness, power consumption efficiency is deteriorated and the number of light-emitting diodes required to obtain a desired white brightness value is increased. Then, problems of increase of a cost and the like arise inevitably.
Accordingly, in order to realize a desired chromaticity of white while the light-emitting diodes of respective colors are being energized efficiently, there is proposed an arrangement in which chip areas of the light-emitting diodes for emitting respective lights of colors of R, G and B are made different. See, Japanese Published Patent Application No. 11-162233.
Further, there is proposed an arrangement in which chromaticity distributions of several sets of groups may be equalized by changing the arrangement of the light-emitting diodes of respective colors so that asymmetry of chromaticity can be improved. See, Japanese Published Patent Application No. 11-3051.
For example, if the light-emitting diode chips of three colors of R, G and B are disposed in a delta fashion as shown in FIG. 1A or if they are disposed in an in-line fashion as shown in FIG. 1B, even when a large number of small-sized light-emitting diodes are disposed, three colors can easily be mixed to provide white light insofar as the respective chips are disposed closely. Therefore, the above-mentioned problem is difficult to arise.
On the other hand, as shown in FIGS. 2A, 2B and 2C, if a single substantially conical reflective surface is disposed relative to one set of the light-emitting diodes of three colors of R, G and B, then predetermined angular extents of the lateral direction become the reflection areas of respective colors of R, G and B relative to the central axis of the cone so that unevenness in brightness and unevenness in chromaticity of reflected light tends to be emphasized too much.
Specifically, as shown in FIG. 2A, if a substantially conical member 51 of which surface is formed as a reflective surface is disposed on the central position of the R, G and B chips disposed like a delta, then as FIG. 2B shows a cross-sectional view seen from the direction shown by an arrow A in FIG. 2A, light emitted from the light-emitting diode of each chip is reflected on the reflective surface of the substantially conical member 51 and thereby traveled toward the lateral direction so as to move away from the central position.
Consequently, as FIG. 2C shows a plan view, the circumference of the R, G and B chips is divided into three areas of an R main light-emitting area, a G main light-emitting area and a B main light-emitting area. In these R, G and B main light-emitting areas, intensity of each emitted light is increased in particular so that it becomes difficult to sufficiently mix those emitted lights to provide white light even when they are passed through the diffuser.
Further, if the optical member having the substantially conical reflective surface, the arrangement (arrangement in which the chip areas are made different) described in the Cited Patent Reference 3) and the arrangement (arrangement in which the arrangements of emitted colors are changed at every set) described in the Cited Patent Reference 4 are simply combined, then unevenness in chromaticity tends to occur.